Hot Rod Forum banner
81 - 100 of 149 Posts

·
Registered
Joined
·
68 Posts
Discussion Starter · #81 ·
Not much vacuum - just a touch. Just enough to feel a little difference as your thumb is pulled off. Leave your thumb over the hole for maybe 10-20 seconds to let vacuum build up. Never quantitated it. If the hose was connected to the air cleaner and air cleaner didn't have oil in it, you may be fine on blow-by.
Hi, Yes the vacuum is stronger at 2000rpm than idle. I held a cloth rag to it and it pulled it in.
Also where that 3/4" hose goes into the valve cover opening, at 2000 revs there's no oil spitting out.
Is the PCV valve suppose to rattle soo much at idle, its continuously rattler.
 

·
******* Professional
Joined
·
1,390 Posts
Hi, Yes the vacuum is stronger at 2000rpm than idle. I held a cloth rag to it and it pulled it in.
Also where that 3/4" hose goes into the valve cover opening, at 2000 revs there's no oil spitting out.
Is the PCV valve suppose to rattle soo much at idle, its continuously rattler.
It would only rattle if the vacuum is not steady. Put a vacuum gauge on it and take a video for us please. You can use that port on the hose near the distributor.

Sent from my moto g power using Tapatalk
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #83 ·
And there's another question. The AFB Carter carb has a 3/8" port coming out the top on the same side as the choke and from what i've seen on the net, its for emissions and it is connected to the Cannister.
but the other cannister ports are open and the air is just blowing out the middle port of the cannister.
So is this a vacuum leak too, or do I just cap it??
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #84 ·
It would only rattle if the vacuum is not steady. Put a vacuum gauge on it and take a video for us please. You can use that port on the hose near the distributor.

Sent from my moto g power using Tapatalk
I am sorry buddy, I don't have a vacuum gauge. embarrassing!
 

·
******* Professional
Joined
·
1,390 Posts
I am sorry buddy, I don't have a vacuum gauge. embarrassing!
Here in the USA we can borrow tools from local parts stores for free (with deposit). Do you have anything like that? Trying to help but you need to do your part.

Sent from my moto g power using Tapatalk
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #86 ·
Here in the USA we can borrow tools from local parts stores for free (with deposit). Do you have anything like that? Trying to help but you need to do your part.

Sent from my moto g power using Tapatalk
yeah, i hear ya. Here in ireland, they loan u nothing.
As i said before u guys don't know how lucky u are.
there is no parts chain stores here, just independent stores, so no competition. No NAPA, AutoZone, CAP, etc..
But i can buy one if necessary, if not here, then online.
Could i approach it a different way. If the vacuum is irregular what does that mean?
And what about that other line to the cannister, it might as well be open, does it matter?
Is it causing the vacuum problem? I attached a picture of it. It sort of points down slightly.
Thanks

Automotive tire Motor vehicle Rim Automotive exterior Automotive fuel system
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #87 ·
Is this what u mean, seen a video on youtube, so i understand why u are suggesting it.
Any ideas on that emissions port, can I cap it or what do you guys suggest?
Gauge Clock Font Measuring instrument Circle
 

·
******* Professional
Joined
·
1,390 Posts
Is this what u mean, seen a video on youtube, so i understand why u are suggesting it.
Any ideas on that emissions port, can I cap it or what do you guys suggest?
Yes, that is a suitable vacuum gauge.

Irregular vaccum could mean a lot of things but mainly want to do a quick check on an intake valve leaking back into the intake - it would be a severe vacuum fluctuation. Just a misfire would be less severe - why I wanted the video. Probably you are heading towards a compression test after that but we can wait and see.

I believe that big port in your photo is a fuel bowl vent "G" on the emissions label in the link below. Maybe the photo in this ad will help (emissions label for 1981 4.9l Trans Am) New 1981 Pontiac Firebird Trans Am Emissions Decal-Label-TA 4.9/301 Non-Turbo | eBay

Remember this label is for "USA Federal Emissions" for a 1981 301 Pontiac non-turbo motor. Should be similar but not exact to your 305. Evaporative emissions should be very similar. Look at your own label if you have it.
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #89 ·

·
Rod...from a Chrysler?
Joined
·
5,769 Posts
If you're not sure, cap it until you stop all vacuum leaks.

Vacuum is not affected by anything except engine operation. It gets created as the piston is going down the cylinder with the intake valve open. When you have a vacuum leak, air is bypassing the carb causing rough running.
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #92 ·
Ordered a vacuum gauge test kit, so should have that in a week or so.
Noticed the brake sensor is broken off the brake manifold assembly, wire is still attached.
Is there anyway to fix it? And is it necessary? Not sure what it does. Picture attached.
Automotive tire Motor vehicle Hood Vehicle Automotive exterior
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #93 ·
If you're not sure, cap it until you stop all vacuum leaks.

Vacuum is not affected by anything except engine operation. It gets created as the piston is going down the cylinder with the intake valve open. When you have a vacuum leak, air is bypassing the carb causing rough running.
ok i'll try that and see how it goes. Thanks
 

·
Rod...from a Chrysler?
Joined
·
5,769 Posts
The brake switch and lamp only go off when they fail.
I'll guarantee you'll know all about it when that happens.
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #95 ·
The brake switch and lamp only go off when they fail.
I'll guarantee you'll know all about it when that happens.
so does that mean the light is only an indicator (idiot light) and is not necessary to the brake operation?
 

·
******* Professional
Joined
·
1,390 Posts
so does that mean the light is only an indicator (idiot light) and is not necessary to the brake operation?
This brake switch would indicate an imbalance in the hydraulic pressures front to rear in the split brake system. Its a bad situation. Light does not control anything.

Sent from my moto g power using Tapatalk
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #97 ·
ok,
Can it be fixed or can i solder the spring back into position?
Or just forget about it as its only an indicator light and controls nothing?
Thanks
 

·
Rod...from a Chrysler?
Joined
·
5,769 Posts
For warning light only.
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #99 ·
Hi, long time no speak. Fitted some parts today.
Hooked up fuel pressure gauge and it read 7psi.
Fitted Holley Regulator and dry gauge and adjusted it down to 4.5psi.
I noticed that the car is only idling at 500rpm now, was about 650rpm before.
Is this because the lower pressure is pushing less fuel through at idle??
Do i now need to adjust idle up on carb, or leave as is?

Speedometer Gauge Measuring instrument Motor vehicle Font


Tire Automotive tire Wheel Hood Bicycle tire
 

·
Rod...from a Chrysler?
Joined
·
5,769 Posts
Yes, adjust it wherever it wants to idle smoothly.
The carb, not the fuel pressure of course.
 
81 - 100 of 149 Posts
Top